Support structure

ABSTRACT

A grid support structure comprising a pair of collinear first support beams of thermally expandible material, and a pair of collinear second support beams of thermally expandible material which are perpendicular to the first support beams and the adjacent ends of which are secured to the adjacent ends of the first support beams. Longitudinal slits are formed in the first beams, each slit extending from the end of the appropriate beam to a position between the ends thereof with the portions of the beam bounding the slit disposed in different planes. Corresponding slits are formed in the second beams or, alternatively, outwardly directed lugs, by means of which the second beams are secured to the first beams are presented by each first beam and are secured to the second beams at positions spaced from the first beam. Longitudinal thermal expansion of the second beams causes the portions of each first beam bounding the slit therein to be urged into overlapping relationship, longitudinal thermal expansion of the first beams similarly causing the portions of each second beam bounding the slit therein to be urged into overlapping relationship, or causing the lugs to flex relative to the first and second beams, as the case may be.

lUite States Patent [72] Inventor Charles 6- Shepherd Onkvllle, Ontario, Canada 211 Appl. No 874,138 [22] Filed Nov. 6, 1969 {45] Patented July 6,1971 [73] Assignee Wilson Lighting Limited Toronto, Ontario, Canada [54] SUPPORT STRUCTURE 12 Claims, 7 Drawing Figs.

[52] US. Cl 52/573, 52/484, 287/189.36 [51] lnt.Cl 1504b 1/68, 1504b 5/52 {50] Field of Search 52/232, 573, 664, 484, 666, 720, 475, DIG. 5; 287118936 A [56] References Cited UNITED STATES PATENTS 2,701,679 6/1955 Bibb et al 52/484X 2,920,357 1/1960 Ericson 52/475 X 3,159,252 12/1964 Cotts 52/573 X 3,242,628 3/1966 Jahn 52/573 Primary Examiner Frank L. Abbott Assistant Examiner- Sam D. Burke Attorney-Maybee and Legris AliSTRACT: A grid support structure comprising a pair of collinear first support beams of thermally expandible material, and a pair of collinear second support beams of thermally expandible material which are perpendicular to the first support beams and the adjacent ends of which are secured to the adjacent ends of the first support beams. Longitudinal slits are formed in the first beams, each slit extending from the end of the appropriate beam to a position between the ends thereof with the portions of the beam bounding the slit disposed in different planes. Corresponding slits are formed in the second beams or, alternatively, outwardly directed lugs, by means of which the second beams are secured to the first beams are presented by each first beam and are secured to the second beams at positions spaced from the first beam. Longitudinal thermal expansion of the second beams causes the portions of each first beam bounding the slit therein to be urged into overlapping relationship, longitudinal thermal expansion of the first beams similarly causing the portions of each second beam bounding the slit therein to be urged into overlapping reliatiom ship, or causing the lugs to flex relative to the first and second beams, as the case may be.

PATENTED JUL 6497! SHEET 1 OF 4 FIG.2

INVENTUR.

CHARLES ca. SHEPHERD ATTORNEYS PATENTEU JUL 6187! sum 2 BF 4 FIG.3

INVENTOR. CHARLES GLSHEPH ERD ATTORN EYS PATENTED JUL 6 I97! SHEET 3 BF 4 INVEN'I'UR. CHARLES G. SHEPHERD ATTORNEYS PATENTEDJUL 6|7| SHEET H [1F 4 INVIi'N'IOR CHARLES G. SHEPHERD ATTORNEYS surros'r s'rnucruas This invention is concerned with a support structure such as a structure constituted by a plurality of first support beams which are all disposed in the same direction and a plurality of second support beams which are likewise all disposed in the same direction, this latter direction being, for example, perpendicular to the direction in which the first support beams are disposed. In such a structure the first and second support beams are interconnected so that the structure is in the form of a grid which may be horizontally mounted below a support deck, such as a flooring deck, in a building structure for supporting, for example, the elements of a ceiling, such as a plurality of lighting units.

The support beams constituting a support structure of the type referred to above are generally forined of a thermally expandible material, such as metal, with the result that provision must be made in such structures for accommodating thermal expansion of the support beams caused by these beams being subjected to a high temperature, such as by a fire in the room space or the like below the support structure. If provision is not made for accommodating such thermal expansion of the support beams there is a considerable danger that, in the event of the beams being subjected to fire heat, the beams will buckle and warp longitudinally with the result that fire insulation panels or the like which are normally supported by the beams will no longer be so supported. The result is, of course, that the first may travel from the room space or the like below the support structure to the space above this structure and hence throughout the entire building structure.

Various arrangements have hitherto been proposed and used with the view to overcoming this disadvantage, the most relevant prior arrangement of which the inventor is aware being that disclosed in U.S. Pat. No. 3,242,628 which issued on March 29, R966 to Jahn. In this patent there is disclosed a ceiling panel supporting grid structure comprising comprising main and cross beams each of which is of approximately T- form in cross section. The flanges of each main beam are formed with a plurality of longitudinally extending slots which are in alignment with the position of attachment of the crossbeams to said main beam so that when the crossbeams are subjected to thermal expansion, as a result for example of a fire, the appropriate portions of the flanges of the main beams are caused transversely to buckle thereby to accommodate the expansion of the crossbeams.

This arrangement of Jahn suffers from the disadvantages that the above-mentioned transverse buckling of the flanges of the main beam caused by thermal expansion of the crossbeams, results almost inevitably in spaces being formed between the flanges of the main beam and the tiles or the like supported thereby, these spaces permitting the fire in the room space below the structure to travel to the region above the structure. Thus, the fire or the like is not contained within the room space in which it originates with the result that the fire damage is likely to be much more extensive than would otherwise be the case. As will be appreciated, therefore, the structure disclosed by J ahn suffers from substantially the same disadvantage as support structures, in which no provision is made for accommodating thermal expansion of the support beams constituting the structures.

It is a primary object, therefore, of the present invention to provide a support structure in which the above-mentioned disadvantages of the structure disclosed by Jahn is substantially overcome and in which, more specifically, thermal expansion of the beams constituting the structure results in no significant longitudinal or transverse buckling or warping of the beams, and hence in the formation of no spaces through which fire may travel from below to above the structure.

Furthermore, the structure disclosed by Jahn accommodates thermal expansion of only the crossbeams. Clearly, if both the main and the crossbeams are formed of a thermally expandible material, the main beams, as well as the crossbeams, are subjected to longitudinal thermal expansion when, for example, a fire occurs and it is, accordingly, an object of the preferred embodiments of the present invention to provide a support structure in which thermal expansion of all the beams constituting the structure is accommodated without buckling or warping ofthe beams.

A support structure according to the present invention comprises at least one first support beam and at least one second support beam which is formed of thermally expandible material and an end portion of which is secured to an end portion of the first support beam. A slit is formed in the first support beam, the slit extending longitudinally of this beam from the end of the beam presented by said end portion thereof to a position between the ends of said beam. The portions of the first support beam bounding the slit are disposed in different planes, and the direction of the longitudinal axis of the second support beam has at least a component which is perpendicular to the longitudinal axis of the first support beam and to the plane containing the slit, thereby to permit said portions of the first support beam to be urged into overlapping relationship by longitudinal thermal expansion of the second support beam.

In order that the invention may be more clearly understood and more readily carried into effect the same will now, by way of example, be more fully described with reference to the accompanying drawings in which:

FIG. I is a perspective view from above of a portion of a support structure according to the invention, lighting units mounted on the support structure being shown diagrammatically in chain-dotted lines;

FIG. 2 is an isometric view from above ofa part of the support structure shown in FIG. ll, this view showing the adjacent end portions of a pair of first and a pair of second support beams;

FIG. 3 is a top plan view of the part of the support structure shown in FIG. 2, the beams being shown in their condition when the second support beams are subjected to thermal expansion;

FIG. 4 is a view corresponding to FIG. 3 but showing the beams in their condition when the first support beams are subjected to thermal expansion;

FIG. 5 is a sectional view on the line 5-5 of FIG. 2, but with the coverplate which is shown in an exploded condition in FIG. 2 disposed in its operative condition;

FIG. 6 is a view corresponding to FIG. 2 but showing an alternative embodiment of the invention; and

FIG. 7 is a view corresponding to FIG. 3 but of the alternative embodiment shown in FIG. 6.

Throughout the various views of the drawings like reference numerals are used to denote like parts.

With reference to the drawings, and in panicular FIG. 1 thereof, denotes generally a support structure which comprises a plurality of first support beams l1 and a plurality of second support beams 12, the form and construction of the support structure it) being hereinafter disclosed in greater detail with reference to the remaining views of the drawings. Z13 denotes generally each of a plurality of lighting units which may operatively be supported by the support structure 10. The lighting units 113 form, however, no part of the present invention and the details of construction of these units are, therefore, not further described or illustrated in this application.

With particular reference to FIG. 2, there is therein illustrated a pair of collinear first support beams 11 of thermally expandible material which are disposed in spaced relationship, i.e. which are so disposed that the adjacent ends 14 thereof are spaced apart. FIG. 2 also shows a pair of collinear second support beams 12 of thermally expandible material which are likewise disposed in spaced relationship, the space 15 between the adjacent ends 16 of the second support beams 12 also constituting the space between the adjacent ends 14 of the first support beams 11.

While in the preferred embodiments of the invention as herein described with reference to the accompanying drawings there is a plurality of first support beams 11 and a plurality of second support beams 12, it is to be understood that in alternative embodiments (not shown) there may be only one first support beam 11 and only at least one second support beam 12.

Each first support beam 11, and each second support beam 12, is of inverted channel form in cross section and comprises a web portion 17 together with two substantially parallel depending limb portions 18. The limb portions 18 of each beam 11 or 12 present outwardly directed flange portions I9 which are disposed in a plane substantially parallel to the plane containing the web portion 17 of said beam 11 or 12.

The adjacent ends 14 of the first support beams 11 each present outwardly projecting lugs which are each of approximately triangular form. Each lug 20 is connected to the appropriate limb portion 18 of the beam- 11 from which it is presented, the lug 20 preferably being integral with said beam 11, and having a lower edge 21 which is upwardly inclined in the direction away from said beam Ill and an upper edge 22 which, in the preferred embodiments illustrated in the drawings, is disposed in a plane substantially parallel to the plane containing the web portion 17 of said beam 11. The edge 22 of each lug 20 presents, at a position spaced from the beam 11 from which said lug 20 is presented, an upwardly projecting tab 23 which is disposed through a slot 24 formed in the web portion 17 of the appropriate one of the second support beams 12, the underface of the web portion 17 of said second support beam 12 being supported on the edge 22 oflug 20 when the tab 23 is so disposed. Each tab 23 is twisted, out of the plane of the slot 24 through which it is disposed, on the side of the slot 24 remote from the lug 20 thereby to maintain in secured interrelationship the adjacent end portions of the first and second support beams 11 and 12. In FIG. 2, the two left-hand tabs 23 are shown in their condition prior to this twisting, the two right-hand tabs 23 being, however, shown in the twisted condition.

The flange portions 19 of each second support beam 12 are each, at the end 16 of the beam 12, off set in the upward direction thereby to overlie, in the manner shown at 25 in FIG. 2, the adjacent flange portion 19 of the appropriate one of the first support beams 11, the flange portions 19 of the beams 11 being at the end 14 thereof of chamfered. form.

Each lug 20 is capable of flexing relative to the second support'beam 12 to which it is secured, and also relative to the first support beam 11 from which it is presented.

A slit 26 is formed in the web portion 17 of each first support beam 11, the slit 26 extending longitudinally of the beam 11 from the end 14 thereof to a position between said end 14 and the other end (not shown) of the beam 1 1. The portions of the web portion 17 of each beam 11 which bound the slit 26 formed therein are disposed in different planes, for example, by downwardly deflecting one of these portions as indicated at 27 in FIG. 2.

The end of each slit 265 remote from the end 14 of the beam 11 in which said slit is formed is in communication with an enlarged opening 28 formed in the web portion 17 of said beam. The openings 28 may be of circular form as shown at the lefthand side in FIG. 2, or may be of elongated form disposed transversely to the longitudinal axis of the beam 11 as shown at the right-hand side of FIG. 2. Particularly in the latter case, the openings 28 serve so to weaken the end portions of the beams 11 in which they are formed that overlapping of the portions of the web portion 17 of each beam II which bound the slit 26 formed therein is facilitated, such overlapping being caused by longitudinal thermal expansion of the beams 12 as is hereinafter more fully described. Furthermore, in both cases, the opening 28 serves to prevent longitudinal creepage of the end of the slit 26 remote from the end 14 of the beam 11 in which it is formed.

As shown at the right-hand side of FIG. 2, a support tie member constituted by a rod 29 may be disposed through the opening 28, the lower end of the rod 29 being screw-threaded and having a washer 30 and a nut 31 mounted thereon below the web portion 17, thereby to support the beam 11 by the rod 29, the upper end (not shown) of which is secured to, for example, a flooring support deck.

As an alternative to supporting the beam 11 by the rod 29 and the associated washer 30 and nut 31, the beam 11 may be supported by means of a tie wire 32 and a strap 33 as shown at the left-hand side of FIG. 2, the strap 33 being disposed through aligned slots 34 formed in the limb portions 18 of the beam 11, with the lower end portion of the wire 32 being secured through openings 35 formed in the end portions of the strap 33.

The second support beam 12 are disposed substantially perpendicular to the first support beams 11, and to the plane containing the slits 26 in the web portions 17 of the first support beams 11, i.e. with the plane containing the slits 26 and disposed perpendicular to the plane containing the web portions 17 of the beams 11. It is not essential, however, that the second support beams 12 be so disposed provided that the direction of the longitudinal axis of each second support beam 12 has at least a component which is perpendicular to the longitudinal axis of each first support beam 11 and to said plane containing the slits 26 in the web portions 17 of the first support beams 11. Thus, in alternative embodiments (not shown) of the invention, each second support beam 12 may be so disposed that the direction of the longitudinal axis thereof forms an acute angle with the longitudinal axis of one of the first support beams 11 and additionally, or alternatively, forms an acute angle with said plane containing the slits 26 in the web portions 17 of the first support beams 1 l,

A cover plate 36 is mounted over the space 15 between the adjacent ends 14 of the beams 11, and the adjacent ends 16 of the beams 12, the cover plate 36 which is shown in an exploded condition in FIG. 2 extending over the adjacent end portions of the first support beams 11 and being connected thereto by means of downwardly projecting tabs 37 which frictionally grip the opposed limb portions 18 of the beams 11 in the manner most clearly shown in FIG. 5. Slits 38 are formed in the end portions of the cover plate 36 which extend over the adjacent end portions of the beams 11, a portion 39 (FIG. 5) of the plate 36 bounding each slit 38 being in engagement with the slit 26 formed in the adjacent beam 11 to maintain the portions of the web portion 17 of said beam 11 bounding the slit 26 therein in different planes.

' As is most clearly shown in FIG. 3, longitudinal thermal expansion of the second support beams 12, Le. longitudinal movement of the end portions of the beams 12 shown in FIG. 3 in the directions of the arrows A, results in the portions of the web portion 17 of each first support beam 11 which bound the slit 26 formed therein, being urged into overlapping relationship, as shown in FIG. 3, by the arrows B.

As shown in FIG. 4, longitudinal thermal expansion of the first support beams 11, i.e. longitudinal movement of the end portions of the beams 11 shown in FIG. 4 in the directions of the arrows C, results in the above-mentioned flexing of each lug 20 relative to the support beam 11 from which it is presented and relative to the support beam 12 to which it is secured by means of the tab 23. As will be appreciated, the ends 16 of the second support beams 12 are, when the structure 10 is in normal use, preferably spaced a short distance from the first support beams 11 thereby to facilitate such flexing of the lugs 20. It is, however, not essential that the ends 16 of the second support beams 12 be so spaced, since the forces exerted during longitudinal thermal expansion of the beams 11 are, in practice, so large that the above-mentioned flexing of the lugs 20 will, in any event, occur.

Although for clarity, the effect of longitudinal thermal expansion of the beams 12 and of the beams 11 has been in two separate view of the drawings, it will be appreciated that, in practice, these effects occur together where, as will usually be the case, the beams 11 and also the beams 12 are formed of thermally expandible material, such as metal, and are operatively all subjected simultaneously to fire heat.

Thus, longitudinal thermal expansion of the first and second support beams 11 and 12 is accommodated in the structure according to the present invention substantially without any longitudinal or transverse buckling or warping of the beams 11 and 12 constituting the structure, and hence without any substantial risk of spaces, through which fire could travel from below to above the support structure, being formed between the beams 11 and 12 and insulation panels or the like operatively supported thereon.

The alternative embodiment of the invention illustrated in FIGS. 6 and 7, is substantially similar to that illustrated in the preceding views of the drawings and differs therefrom substantially only in that the lugs 20, and associated tabs 23, are omitted and the end portions of the beams 11 are secured to the adjacent end portions of the beams 12 by means of outwardly projecting, hook-shaped members 10 which are presented by the limb portions 18 of the first support beams 11 at the ends 14 thereof and which are engageable with similarly formed outwardly projecting, hook-shaped members 41 presented by the limb portions 18 of the second support beams 12 at the ends 13 thereof, each hook-shaped member 40 being upwardly open and each hook-shaped member 41 being downwardly open so that these members are interconnectably engageable in the manner shown in FIG. 6. Furthermore, in the alternative embodiment illustrated in FIGS, 6 and 7 the web portions 17 of all the beams 11 and 12 are formed with longitudinally extending slits corresponding to the slits 26 formed in the web portions 17 of the beams 11 in the first embodiment. in addition, in this alternative embodiment the slits 38 formed in the coverplate 36 have been omitted although it is to be understood that such slits could also be provided in the coverplate 36 in this alternative embodiment.

As shown in FIG. 7, longitudinal thermal expansion of the second support beams 12 results in the portions of the web portions 17 of the beams 11 which bound the slits 26 formed therein being urged into overlapping relationship in the same manner as is described above with reference to FIG. 3. In this alternative embodiment, longitudinal thermal expansion of the first support beams 11 results in the portions of the web portions 17 of the beams 12 which bound the slits 26 formed therein being likewise urged into overlapping relationship in an identical manner.

What I claim as my invention is:

1. A support structure comprising a first support beam, and at least one second support beam which is formed of thermally expandible material and an end portion of which is secured to an end portion of the first support beam, a slit being formed in the first support beam and extending longitudinally thereof from the end of the first support beam presented by said end portion thereof to a position between the ends of the first support beam, the portions of the first support beam bounding the slit being in different planes and the direction of the longitudinal axis of the second support beam having at least a component which is perpendicular to the longitudinal axis of the first support beam and to the plane containing the slit, thereby to permit said portions bounding the slit of the first support beam to be urged into overlapping relationship by longitudinal thermal expansion ofthe second support beam.

2. A support structure according to claim 1, wherein at least the first support beam is of inverted channel form in cross sec tion, and comprises a web portion and two substantially parallel depending limb portions, the slit being formed in the web portion ofsaid beam.

3. A support structure according to claim 1, wherein the end of the slit remote from said end of the first support beam is in communication with an enlarged opening formed in the first support beam.

4. A support structure according to claim 3, wherein a sup port tie member is disposed through said enlarged opening, the first support beam being in supported engagement with said member.

5. A support structure according to claim 1, wherein the first support beam is formed of thermally expandible material and the securement between said end portions of the first and second support beams comprises outwardly projecting lug means which is presented by said end portion of the first support beam and which is secured to the second support beam at a position spaced from the first support beam, the lug means being capable of flexing relative to the first support beam and relative to the second support beam, thereby to permit longitudinal thermal expansion ofthe first support beam.

6. A support structure comprising a pair of collinear first support beams which are formed of thermally expandible material and which are disposed in spaced relationship, and a pair of collinear second support beams which are formed of thermally expandible material and which are disposed in spaced relationship with the space th-erebetween constituting the space between the first support beams and with the second support beams being substantially perpendicular to the first support beams, the adjacent ends of the first support beams each presenting outwardly directed luigs which are secured to the second support beams at positions spaced from the first support beams, each lug being capable of flexing relative to the first support beam from which it is presented and relative to the second support beam to which it is secured thereby to permit longitudinal thermal expansion of the first support beams, slits being formed in the first support beams and extending longitudinally thereof from the adjacent ends of said first support beams to positions between the ends thereof, the portions of each first support beam bounding the slit therein being in different planes, and the second support beams being substantially perpendicular to the plane containing the slit in each first support beam, thereby to permit said portions of each first support beam to be urged into overlapping relationship by longitudinal thermal expansion of the second support beams.

7. A support structure according to claim 6, wherein coverplate is mounted over the space between the adjacent ends of the first support beams and the adjacent ends of the second support beams, the coverplate extending over the adjacent end portions of the first support beams and being connected thereto.

8. A support structure according to claim 7, wherein slits are formed in the portions of the coverplate which extend over the adjacent end portions of the first support beams, a portion of the coverplate bounding each slit formed therein being in engagement with the slit formed in the adjacent first support beam to maintain the portions of said first support beam bounding the slit therein in different planes.

9. A support structure according to claim 6, wherein the securement between each lug and the second support beam to which it is secured comprises an upwardly projecting tab presented by the lug and disposed through a slot formed in said second support beam, the tab being disposed out of the plane of the slot on the side of the slot remote from the lug.

10. A support structure comprising a pair of collinear first support beams which are formed of thermally expandible material and which are disposed in spaced relationship, and a pair of collinear second support beams which are formed of thermally expandible material and which are disposed in spaced relationship with the space therebetween constituting the space between the first support beams and with the second support beams being substantially perpendicular to the first support beams, the adjacent ends of the first support beams being secured to the adjacent ends of the second support beams, slits being formed in the first and second support beams and extending longitudinally thereof from the adjacent ends of the beams to positions between the ends thereof, and the portions of each first and second support beam bounding the slit therein being in different planes, thereby to permit said portions of each first and second support beam to be urged into overlapping relationship by longitudinal thermal expansion ofthe second and first support beams, respectively.

11. A support structure according to claim 10, wherein a coverplate is mounted over the space between the adjacent ends of the first support beams and the adjacent ends of the second support beams, the coverplate extending over the adjacent end portions of the first support beams and being connected thereto.

12. A support structure according to claim 1 1, wherein slits are formed in the portions of the coverplate which extend over the adjacent end portions of the first support beams, a portion of the coverplate bounding each slit formed therein being in 

1. A support structure comprising a first support beam, and at least one second support beam which is formed of thermally expandible material and an end portion of which is secured to an end portion of the first support beam, a slit being formed in the first support beam and extending longitudinally thereof from the end of the first support beam presented by said end portion thereof to a position between the ends of the first support beam, the portions of the first support beam bounding the slit being in different planes and the direction of the longitudinal axis of the second support beam having at least a component which is perpendicular to the longitudinal axis of the first support beam and to the plane containing the slit, thereby to permit said portions bounding the slit of the first support beam to be urged into overlapping relationship by longitudinal thermal expansion of the second support beam.
 2. A support structure according to claim 1, wherein at least the first support beam is of inverted channel form in cross section, and comprises a web portion and two substantially parallel depending limb portions, the slit being formed in the web portion of said beam.
 3. A support structure according to claim 1, wherein the end of the slit remote from said end of the first support beam is in communication with an enlarged opening formed in the first support beam.
 4. A support structure according to claim 3, wherein a support tie member is disposed through said enlarged opening, the first support beam being in supported engagement with said member.
 5. A support structure according to claim 1, wherein the first support beam is formed of thermally expandible material and the securement between said end portions of the first and second support beams comprises outwardly projecting lug means which is presented by said end portion of the first support beam and which is secured to the second support beam at a position spaced from the first support beam, the lug means being capable of flexing relative to the first support beam and relative to the second support beam, thereby to permit longitudinal thermal expansion of the first support beam.
 6. A support structure comprising a pair of collinear first support beams which are formed of thermally expandible material and which are disposed in spaced relationship, and a pair of collinear second support beams which are formed of thermally expandible material and which are disposed in spaced relationship with the space therebetween constituting the space between the first support beams and with the second support beams being substantially perpendicular to the first support beams, the adjacent ends of the first support beams each presenting outwardly directed lugs which are secured to the second support beams at positions spaced from the first support beams, each lug being capable of flexing relative to the first support beam from which it is presented and relative to the second support beam to which it is secured thereby to permit longituDinal thermal expansion of the first support beams, slits being formed in the first support beams and extending longitudinally thereof from the adjacent ends of said first support beams to positions between the ends thereof, the portions of each first support beam bounding the slit therein being in different planes, and the second support beams being substantially perpendicular to the plane containing the slit in each first support beam, thereby to permit said portions of each first support beam to be urged into overlapping relationship by longitudinal thermal expansion of the second support beams.
 7. A support structure according to claim 6, wherein coverplate is mounted over the space between the adjacent ends of the first support beams and the adjacent ends of the second support beams, the coverplate extending over the adjacent end portions of the first support beams and being connected thereto.
 8. A support structure according to claim 7, wherein slits are formed in the portions of the coverplate which extend over the adjacent end portions of the first support beams, a portion of the coverplate bounding each slit formed therein being in engagement with the slit formed in the adjacent first support beam to maintain the portions of said first support beam bounding the slit therein in different planes.
 9. A support structure according to claim 6, wherein the securement between each lug and the second support beam to which it is secured comprises an upwardly projecting tab presented by the lug and disposed through a slot formed in said second support beam, the tab being disposed out of the plane of the slot on the side of the slot remote from the lug.
 10. A support structure comprising a pair of collinear first support beams which are formed of thermally expandible material and which are disposed in spaced relationship, and a pair of collinear second support beams which are formed of thermally expandible material and which are disposed in spaced relationship with the space therebetween constituting the space between the first support beams and with the second support beams being substantially perpendicular to the first support beams, the adjacent ends of the first support beams being secured to the adjacent ends of the second support beams, slits being formed in the first and second support beams and extending longitudinally thereof from the adjacent ends of the beams to positions between the ends thereof, and the portions of each first and second support beam bounding the slit therein being in different planes, thereby to permit said portions of each first and second support beam to be urged into overlapping relationship by longitudinal thermal expansion of the second and first support beams, respectively.
 11. A support structure according to claim 10, wherein a coverplate is mounted over the space between the adjacent ends of the first support beams and the adjacent ends of the second support beams, the coverplate extending over the adjacent end portions of the first support beams and being connected thereto.
 12. A support structure according to claim 11, wherein slits are formed in the portions of the coverplate which extend over the adjacent end portions of the first support beams, a portion of the coverplate bounding each slit formed therein being in engagement with the slit formed in the adjacent first support beam to maintain the portions of said first support beam bounding the slit therein in different planes. 